1. Field of the Invention
The present invention relates to a semiconductor switch driving circuit, particularly relates to a semiconductor switch driving circuit suitable for controlling a semiconductor switch used for electrotherapy apparatus such as a defibrillator.
2. Related Art
For a device for a semiconductor switch which enables the control of high voltage, an insulated gate bipolar transistor (IGBT) is generally used.
A circuit for driving a semiconductor switch configured by this insulated gate bipolar transistor (hereinafter called IGBT) is connected via a photocoupler or a transformer so that the circuit is electrically insulated from a circuit part that directly drives a control signal and the gate of IGBT.
Referring to drawings, an example using a photocoupler and an example using a pulse transformer respectively of a conventional type semiconductor switch driving circuit will be described below.
FIG. 3 is a circuit diagram showing a semiconductor switch driving circuit using a photocoupler.
As shown in FIG. 3, a part that drives a switching device (IGBT) 208a at a first stage is composed of a photocoupler 201a, a comparator 202a, a positive voltage source 203a, transistors 204a and 205a, a negative voltage source 206a and a resistor 207a and a ground terminal is connected to a GND1. Also, a part that drives a switching device (IGBT) 208b at a second stage is composed of a photocoupler 201b, a comparator 202b, a positive voltage source 203b, transistors 204b and 205b, a negative voltage source 206b and a resistor 207b, a ground terminal is connected to a GND2 and a driving circuit at the next stage or at the subsequent stages can be similarly composed.
FIG. 4 is a circuit diagram showing a semiconductor switch driving circuit using a pulse transformer.
As shown in FIG. 4, a part that drives a switching device (IGBT) 257a at a first stage connected to a secondary side of a pulse transformer 251 is composed of a transistor 255a, diodes 252a and 253a and resistors 254a and 256a, a part that drives a switching device (IGBT) 257b at a second stage is composed of a transistor 255b, diodes 252b and 253b and resistors 254b and 256b and a driving circuit at the next stage or the subsequent stages can be similarly composed.
However, the conventional type semiconductor switch driving circuit has the following problems.
The semiconductor switch driving circuit shown in FIG. 3 is provided with the photocoupler, the positive voltage source, the negative voltage source and the GND at every stage of a driven switching device (IGBT). In a conventional type system of a multistage semiconductor switch, there is a problem of a time lag in the switching of a switching device (IGBT). When the timing of the switching is delayed, overvoltage is applied to a switching device in case switching devices are connected in series as shown in FIG. 3, also, in case switching devices are connected in parallel, over current is applied to a switching device and in any case, the switching device may be broken. Also, as the same number of the photocouplers, the positive voltage sources, the negative voltage sources and the grounds as the number of the stages of the switching devices (IGBT) are required, there is a problem that the scale of the circuit is large and the cost of the whole apparatus is high.
Also, the semiconductor switch driving circuit shown in FIG. 4 cannot continuously supply positive voltage or negative voltage to the gate of the switching device (IGBT) to be driven. There is also a problem that switching to reverse bias (from positive voltage to negative voltage or from negative voltage to positive voltage) is slow.
Further, there are problems that positive voltage or negative voltage cannot be made to an independent value and the size of a transformer for low-frequency switching is large.
The invention is made to solve the problems of the prior art and the object is to provide a semiconductor switch driving circuit suitable for controlling a semiconductor switch which can continuously supply positive voltage or negative voltage to the gate of a switching device (IGBT) to be driven by the small number of parts, enables high-speed switching to reverse bias and is particularly used for electrotherapy apparatus because a lag in switching timing between each stage can be reduced.
To achieve the object, a semiconductor switch driving circuit according to a first aspect of the invention is based upon a semiconductor switch driving circuit provided with at least a transformer and is characterized in that a primary side area for controlling the primary current of the transformer according to a control signal for controlling a semiconductor switch is provided on the primary side of the transformer, a secondary side area for directly driving a switching device is provided on the secondary side of the transformer, voltage between the gate and the emitter of the switching device can be continuously kept positive, voltage between the gate and the emitter can be continuously kept negative and voltage between the gate and the emitter can be switched so that it is alternately positive and negative.
A semiconductor switch driving circuit according to a second and a third aspect of the invention is characterized in that the circuit is operated in synchronization with an input control signal because the primary side area is configured so that the primary side area receives a control signal, transmits power for controlling plural switching devices to the secondary side area and absorbs back electromotive force caused when current flowing in the transformer is cut off and the secondary side area is configured so that the secondary side area receives the power supplied from the primary side area, transmits the power for controlling the plural switching devices to the plural switching devices, the plural switching devices receive the power supplied to the secondary side area of the semiconductor switch driving circuit and cause or prevent current to flow for switching.
A semiconductor switch driving circuit according to a fourth aspect of the invention is characterized in that back electromotive force between a terminal at one end of a primary winding of a transformer and a terminal at the other end of the primary winding of the transformer can be inhibited by connecting the source of P channel MOSFET to a power terminal, connecting the drain of the P channel MOSFET to the anode of a diode, connecting the cathode of the diode to the terminal at one end of the primary winding of the transformer and as a result, conducting the P channel MOSFET.
A semiconductor switch driving circuit according to a fifth aspect of the invention is characterized in that when the primary side area receives an input control signal, it transmits power for controlling plural switching devices to a secondary side area and absorbs back electromotive force caused when current flowing in the transformer is cut off because a control signal input terminal is connected to the base of an NPN bipolar transistor via a resistor and a capacitor respectively connected in parallel, the base and the emitter of the NPN bipolar transistor are connected via a resistor, the emitter is connected to a ground terminal, the collector of the NPN bipolar transistor is connected to the gate of a P-channel MOSFET via a resistor, the gate and the source of the P-channel MOSFET are connected via a resistor, the source is connected to a power terminal, the drain of the P-channel MOSFET is connected to the anode of a diode, the cathode of the diode is connected to the drain of a N-channel MOSFET and a terminal of a primary winding of a transformer, the gate and the source of the N-channel MOSFET are connected via a resistor, the source is connected to a ground terminal, a control signal input terminal is connected to the gate of the N-channel MOSFET via a resistor, a control signal input terminal is connected to the base of an NPN bipolar transistor via a resistor and a capacitor respectively connected in parallel, the base and the emitter of the NPN bipolar transistor are connected via a resistor, the emitter is connected to a ground terminal, the collector of the NPN bipolar transistor is connected to the gate of a P-channel MOSFET via a resistor, the gate and the source of the P-channel MOSFET are connected via a resistor, the source is connected to a power terminal, the drain of the P-channel MOSFET is connected to the anode of a diode, the cathode of the diode is connected to the drain of a N-channel MOSFET and a terminal of the primary winding of the transformer, the gate and the source of the N-channel MOSFET are connected via a resistor, the source is connected to a ground terminal, a control signal input terminal is connected to the gate of the N-channel MOSFET via a resistor, terminals of the primary winding of the transformer are connected to a center tap, the center tap is connected to a power terminal and the center tap is connected to a ground terminal via a capacitor.
A semiconductor switch driving circuit according to a sixth aspect of the invention is characterized in that the withstand voltage against the application of high voltage to a semiconductor switch is a value acquired by adding the withstand voltage of the switching device itself at each stage because the secondary side area is provided with plural switching devices and plural gate driving sections that directly drives the switching device and the plural switching devices are connected in series.
A semiconductor switch driving circuit according to a seventh aspect of the invention is characterized in that as the switching device is made of an insulated gate bipolar transistor (IGBT), it is a device (IGBT) provided with both the low-saturation voltage characteristic of a bipolar transistor and the switching characteristic of power MOSFET.
A semiconductor switch driving circuit according to an eighth aspect of the invention is characterized in that a Zener diode for preventing electromotive force generated on a secondary winding by back electromotive force caused on a primary winding of the transformer is provided to the secondary side area.
A semiconductor switch driving circuit according to aninth aspect of the invention is characterized in that the secondary side area receives power supplied from a primary side area and transmits the power for controlling plural switching devices to the plural switching devices because a terminal at one end of a secondary winding of the transformer is connected to a first Zener diode, a second Zener diode is connected to the gate of a specific switching device via a first resistor, same kind of polarities of the first and the second Zener diode are directly connected in series with the polarities face to face, a terminal at the other end of the secondary winding of the transformer is connected to the emitter of the specific switching device, a second resistor and a capacitor are connected between the second Zener diode and the emitter of the specific switching device and a structure comprising the secondary windings of the transformer and the switching device connected via the gate driving section is plurally provided.
An electrotherapy apparatus according to a tenth aspect of the invention is characterized in that the semiconductor switch driving circuit according to any of the first to the ninth aspects of the invention is used for a semiconductor switch having a circuit for generating a high-voltage electric pulse and a high-voltage electric pulse is supplied to an outside living body from an output terminal of the electrotherapy apparatus.